Fire retardant curable ethylenically unsaturated compositions

ABSTRACT

A composition comprising a curable, ethylenically unsaturated compound containing ester linkages and an effective fire retardant amount of N,N&#39;-ethylene bis(salicylidene iminato) FE II, its oxidation product, or a mixture thereof, is disclosed. Also disclosed is a process for rendering fire retardant a curable ethylenically unsaturated composition containing ester linkages comprising adding to said composition an effective fire retardant amount of N,N&#39;-ethylene bis(salicylidene iminato) FE II, its oxidation product, or a mixture thereof.

BACKGROUND OF THE INVENTION

This invention relates to fire retardant, curable, ethylenicallyunsaturated compositions containing ester linkages. This invention alsorelates to a process for rendering fire retardant a curable,ethylenically unsaturated composition containing ester linkages.

Fire retardant, curable, ethylenically unsaturated compositions areknown from, inter alia, U.S. Pat. No. 4,013,815. The compositionscontain unsaturated polyester resin which is cured by copolymerizationof an unsaturated polyester and an ethylenically unsaturated monomer.Most iron compounds mentioned in the U.S. patent, such as ferricacetate, ferric formate, and ferrous tartrate, when added in an amountof 0.55 to about 50 percent, by weight, based on unsaturated polyester,are found to be fire retardant only to such a degree that at least 4.4percent, by weight, of halogen, based on the amount of cured polyesterresin must still be present in order for the compositions to beeffectively fire retardant.

In view of the increasingly stringent demands made on industrialproducts, especially with respect to their effect on the environment,there is a very great need for unsaturated polyester resin compositionswhich have been made fire retardant without the inclusion of halogencompounds.

In view of the foregoing, an object of this invention is to providecurable, ethylenically unsaturated compositions containing esterlinkages which have been made sufficiently fire retardant without thenecessity for including a halogen compound.

SUMMARY OF THE INVENTION

There has now been discovered a composition comprising a curable,ethylenically unsaturated compound containing ester linkages and aneffective fire retardant amount of N,N'-ethylene bis(salicylideneiminato) FE II, its oxidation product, or a mixture thereof.

There has also been discovered a process for rendering fire retardant acomposition containing a curable, ethylenically unsaturated compoundcontaining ester linkages. The process comprises adding to saidcomposition an effective fire retardant amount of N,N'-ethylenebis(salicylidene iminato) FE II, its oxidation product, or a mixturethereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The compound N,N'-ethylene bis(salicylidene iminato) FE II, which hasalso been referred to in literature as bis(salicylidene) ethylenediimino iron (II), will, for the sake of brevity, be referred tohereinafter as Fe (salen). The oxidation product derived from Fe (salen)may be expressed by the formula [Fe (salen)]₂ O. The structure of thelatter compound is described in Coordination Chemistry Reviews, 9(1972-1973) 311-337, Elsevier Scientific Publishing Company, Amsterdam.

Fe (salen) and [Fe (salen)]₂ O are both soluble in ethylenicallyunsaturated compositions which are based on an ester group-containingcompound and can be readily incorporated into it directly. Thepreparation of the compound may be performed as indicated in ChemicalAbstracts 49, 5186 i(1955) for the corresponding cobalt compound,utilizing iron chloride, salicylaldehyde, and ethylenediamine.

It is extremely surprising that the iron compounds which are utilized inthe practice of the present invention impart greatly enhanced fireretardancy to the present products upon the curing thereof, but havevery little detrimental effect on the curing of the compounds. From theresults of comparative experiments it has been determined that, forinstance, the ferrous and ferric acetyl acetonates mentioned in U.S.Pat. No. 4,013,815, which are also known by the terms2,4-pentanedione-Fe II and 2,4-pentanedione-Fe III, do display astrongly fire retardant effect in polyester resin compositions whichcontain very little, if any halogen, but are not suitable for thepresent purpose because of too rapid curing (see Table IV hereinbelow).Although the foregoing drawback may be minimized by taking specialprecautions, such an encapsulation, it will become evident that somesolutions will encounter a large number of practical and economicdrawbacks.

Of the curable, ethylenically unsaturated compositions based on an estergroup-containing compound which may be used in accordance with thepresent invention for the preparation of fire retardant material,particularly suitable are those which are derived from a polycarboxyliccompound and a polyhydric alcohol. Within the scope of the presentinvention polycarboxylic compounds include, for example, polycarboxylicacids, polycarboxylic anhydrides, polycarboxylic halides, andpolycarboxylic esters. The unsaturation may be provided in thepolycarboxylic compound or in the alcohol or in both. Typically theunsaturation is provided in one or more ethylenically unsaturatedpolycarboxylic compounds such as maleic acid, fumaric acid, ethylmaleicacid, itaconic acid, citraconic acid, mesaconic acid, and aconitic acid,or the acid chlorides, esters, or anhydrides derived therefrom.

Examples of typical ethylenically unsaturated alcohols include2-butene-1,4-diol, 2-pentene-1,5-diol, and the unsaturated hydroxyethers such as glycerol monoallyl ether and pentaerythritol diallylether.

The saturated polycarboxylic compounds which are suitable for use of thepreparation of the present polyester resins may be derived from analiphatic, cycloaliphatic, aromatic, or heterocyclic group. Examples ofthe foregoing include phthalic acid, isophthalic acid, terephthalicacid, adipic acid and/or succinic acid and the acid halides, acidanhydrides, and esters derived therefrom.

Examples of suitable saturated polyvalent alcohols include ethyleneglycol, diethylene glycol, propylene glycol, dipropylene glycol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,2,2,4-trimethylpentane-1,3 diol, 1,4 cyclohexane dimethanol, glycerol,mannitol, sorbitol, substituted bisphenols, 2,2-bis(4-hydroxycyclohexyl)propane, and mixtures of the foregoing compounds.

Although the presence of halogen in the unsaturated compositionsaccording to the present invention is not necessary in order to obtainfire retardant properties, the presence, in itself of halogen--forinstance to obtain certain physical and/or chemical properties--is notexcluded from the scope of the present invention.

Halogenated acids which may be used in the preparation of unsaturatedpolyester resins include tetrachlorophthalic acid and diclorosuccinicacid. Examples of halogenated alcohols include2,3-difluorobutane-1,4-diol and 2,2-dichloromethyl propane-1,3-diol.

Moreover, the properties of unsaturated polyesters may still be modifiedby the incorporation therein of suitable monofunctional carboxylic acidsand/or alcohols. Examples of suitable alcohols include2,2-dichloroethanol and 1,1,1-trifluoropropane-2-ol. Examples ofmonofunctional acids include lauric acid and oleic acid.

Furthermore, the properties of unsaturated polyesters can be endlesslyvaried by the use of various types of acids and alcohols such as anunsaturated acid, a saturated acid, and a saturated alcohol.

In the preparation of unsaturated polyesters the starting materialsgenerally used are maleic acid, maleic anhydride, or fumaric acid andethylene glycol, 1,2-propylene glycol, or 1,3-butane diol. In additionto using bifunctional alcohols and acids in the formation of unsaturatedpolyesters, compounds having a combined hydroxyl and carboxyl functionmay be employed. In this respect, use may be made of hydroxy-pivalicacid.

If, in addition to bifunctional alcohols or acids, a small proportion oftri- or polyfunctional compounds is allowed to participate in thecondensation, some degree of branching may be obtained. Examples of suchcompounds include 2,3,5-hexane tricarboxylic acid, trimellitic acid,glycerol, trimethylol propane, pentaerythritol, and tris-β-hydroxyethylisocyanurate. In addition, the unsaturated polyesters may still containgroups other than ester groups, such as amide, imide, and urethanegroups. Thus, the molecular weight of polyesters can be considerablyincreased by reacting the terminal groups with diisocyanates.

The preparation of unsaturated polyesters may take place in the melt orby azeotropic condensation. When use is made of acid anhydrides andepoxides, the preparation in the melt is effected by polyaddition. Thetypical procedure starts from approximately equivalent amounts of acidsand alcohols, which are esterified to the desired molecular weight at170° to 230° C. Use may be made of catalysts such as para-toluenesulphonic acid, benzene sulphonic acid and β-naphthalene sulphonic acid.

The curing of unsaturated polyesters typically takes place in thepresence of an ethylenically unsaturated copolymerizable monomer, suchas styrene, or less often, diallyl phthalate or triallyl cyanurate.Other monomers which may be used in curing are α-methyl styrene, vinyltoluene, 2-chlorostyrene, 2,5-diclorostyrene, para-divinyl benzene,methacrylic methyl ester, acrylic methyl ester, acrylic-tertiary-butylester, acrylonitrile, acrylamide, triacryl formal, vinyl acetate,N-vinyl pyrrolidone, 2-vinyl pyridine, N-vinyl carbazole, and mixturesof the foregoing compounds.

In place of the aforementioned diallyl phthalates, suitable monomersinclude, for example, one or more of the following compounds: diallylfumarate, allyldiglycol carbonate, allyllidene diacetate, dimethallylterephthalate, butane diol diallyl ether, glycerol diallyl etheradipate, and the tetraallyl ether of tetramethylol acetylene diurea.

In addition to the aforementioned typically monomers there may also bepresent other copolymerizable compounds such as maleimide and esters andhalf esters of maleic acid and fumaric acid. Several salts derived fromthe aforementioned half esters and polyvalent metals such as, aluminium,dissolve in polyester resins. The dissolution is often accompanied by aconsiderable increase in viscosity, which may be of importance withrespect to moulding materials. The amount of ethylenically unsaturatedmonomer in the mixture is also chosen so that after polymerization, athermosetting polymer is obtained. Depending upon the desiredproperties, the weight percentage of unsaturated polyester in thepolyester resin may vary from about 10 to about 90 percent, without theuse of any further additives.

The polymerization reaction is generally commenced by a free-radicalinitiating catalyst, resulting in a cross-linked and cured polyesterresin. The temperature at which the reaction is initiated is dependentupon the catalyst system which is utilized. When use is made of cobaltnaphthenate and methylethyl ketone peroxide curing may be effected atroom temperature. The unsaturated polyester and the ethylenicallyunsaturated monomer are preferably mixed at elevated temperature inorder to bring about better dissolution and homogenization. To preventpremature polymerization it is preferable that, prior to the mixingoperation, a polymerization inhibitor be included in the unsaturatedpolyester. Subsequently, a catalyst and, if need be, also an acceleratorare added. The percentage by weight of polymerization inhibitor isgenerally in the range of from about 0.001 to about 1 percent, byweight, of the mixture to be polymerized.

Examples of polymerization inhibitors which may be successfully appliedinclude hydroquinone, benzoquinone, para tertiary butylcatechol,para-phenylene diamine, trinitrobenzene, and picric acid. Examples ofsuitable catalysts include benzoyl peroxide, acetyl peroxide, laurylperoxide, methylethyl ketone peroxide and cumene hydroperoxide. Theamount to be used is dependent on the activity and the presence ofinhibitors and generally varies from about 0.01 to about 10 percent, byweight, based on the amont of resin.

The polymerization reaction may also be promoted by the use ofaccelerators such as metals or metal salts, such as cobalt octoate,cobalt maleate and cobalt naphthenate, or amines such as dimethylamine,dibutylamine, or mercaptans such as dodecyl mercaptan. The acceleratorsare generally employed in the same amount as, or in a smaller amountthan, the catalyst.

It has been found that not only typical unsaturated polyesters, but alsocompositions based on an ethylenically unsaturated ester having thefollowing formula: ##STR1## wherein R₁ and R₂ are independently selectedfrom the group consisting of hydrogen and methyl, and m and n areintegers from about 1.0 to about 3.0, are suitable for the preparationof fire retardant compositions according to the present invention. It ispreferred, however, that as the ethylenically unsaturated ester,2,2-bis-[para-(β-hydroxyethoxy)phenyl] propane dimethacrylate should beused.

Curing may be effected in a manner corresponding to the aforementionedprocess for use with unsaturated polyesters, utilizing a free-radicalinitiator such as a peroxidic compound, an azo compound, or a compoundsuch as hexaphenyl ethane or1,2-diphenyl-1,2-dicyanoethane-1,2-dicarboxylic dimethyl ester.Preferably one should utilize radical initiators which are useful attemperatures in the range from about 60° to about 175° C., preferably inthe range from about 120° to about 160° C. As indicated above for theunsaturated polyesters, curing may also take place at lower temperaturesin the presence of the aforementioned initiators in combination withpolymerization accelerators such as cobalt octoate or amines such asdimethyl aniline. Curing may also be effected by means of UV radiationin the presence of UV-initiators, or by irradiation with acceleratedelectrons, typically known as electron-beam curing.

The organic iron compound Fe (salen), [Fe (salen)]₂ O, and mixturesthereof, may be incorporated into one or more of the reaction componentsat any time prior to curing.

It has been found that along with the other desired properties,sufficient fire retardancy typically may be obtained if the ironcompound is used in an amount from about 0.1 to about 10 percent, byweight, calculated on the mixture of fire retardant additive andcomponents participating in the curing process. It is also possible,however, to use concentrations in the order of, for example, 15 or 20percent.

The concentration at which the best fire retardancy is obtained isdependent upon the composition of the cured compositions. It will not bedifficult for one skilled in the art to establish the optimum rangewithin which maximum protection against fire is obtained. It has beenfound that such a range may be dependent upon whether a filler has beenincluded.

Suitable fillers include various metal oxides, glass fibers, asbestosfibers, mica, colemanite, powdered chalk, powdered quartz, powderedaluminium mica, aluminium oxide, aluminium hydroxide, aluminiumsulphate, wollastonite, ground and precipitated chalk, magnesiumcarbonate, kaolin, titanium dioxide, and talc.

It has also been found that the presence of antimony trioxide, which isoften utilized as a synergist in fire retardant additives for polymers,produces an opposite effect in the compositions of the presentinvention.

The concentration of fillers to be incorporated into the present curablecompositions is dependent upon many factors, including both physical andeconomic considerations. The best fire retardant properties aretypically obtained when the filler is utilized in an amount from about 2to about 60 percent, by weight, based on the mixture of filler andcomponents participating in the curing process in the presence of aniron compound which is itself utilized in an amount from about 0.1 toabout 5 percent, by weight, based on the mixture of fire retardantadditives and components participating in the curing process.

It has been found that a distinctly synergistic effect may result fromthe use of the foregoing combination of substances. For a number ofapplications, the goal will be a cured composition having optimum fireretardant properties obtained at a minimum filler concentration, toachieve the foregoing goal, the present invention provides a curablecomposition containing a filler in an amount of from about 5 to about 20percent, based on the mixture of filler and components participating inthe curing process, in the presence of an amount of iron compound of 0.1to 3.5 percent, by weight, based on the mixture of iron compound andcomponents participating in the curing process.

The present invention is further illustrated by the followingnon-limiting examples:

The fire retardant properties obtained in the following examples weredetermined by measuring the Oxygen Index (OI) in conformity with ASTM D2863-70, unless otherwise indicated. The higher the OI obtained, themore fire retardant is the cured composition. The resins utilized in theexamples were composed as follows:

Resin 1

An unsaturated polyester was prepared from 15.2 parts by weight ofphthalic anhydride; 23.5 parts by weight of maleic anhydride and 27.3parts by weight of propylene glycol. The resulting product was mixedwith 34 parts by weight of styrene, 2 parts by weight of a 50% by weightsolution in water of methyl ethyl ketone peroxide and 0.5 parts byweight of a 1% by weight solution in water of cobalt octoate. Curing for24 hours at 20° C. was followed by after-curing for 2 hours at 120° C.

Resin 2

The unsaturated polyester for this resin was prepared from 22.1 parts byweight of phthalic anhydride; 14.6 parts by weight of maleic anhydride;21.6 parts by weight of propylene glycol and 4.8 parts by weight ofdiethylene glycol. The unsaturated polyester obtained with thesecomponents was mixed with 36.9 parts by weight of styrene; 2 parts byweight of a 50% by weight solution in water of methyl ethyl ketoneperoxide and 0.5 parts by weight of a 1% by weight solution in water ofcobalt octoate. Curing was effected in the manner indicated under Resin1.

Resin 3

The unsaturated polyester was prepared from 19.7 parts by weight ofisophthalic acid; 11.6 parts by weight of maleic anhydride and 24.7parts by weight of neopentyl glycol. The unsaturated polyester thusobtained was mixed with 44 parts by weight of styrene, 2 parts by weightof a 50% by weight solution in water of methyl ethyl ketone peroxide and0.5 parts by weight of a 1% by weight solution in water of cobaltoctoate. Curing was effected as indicated for Resin 1.

Resin 4

The resin was prepared by radical polymerization of 100 parts of2,2-bis-(p-(β-hydroxy-ethoxy)-phenyl) propane dimethacrylate in thepresence of 2 parts of a 40% by weight solution in water of dibenzoylperoxide. Curing took place at a temperature of 70° C. and lasted 24hours, followed by after-curing for 2 hours at 120° C.

Resin 5

The unsaturated polyester for this resin was prepared from 9.8 parts byweight of maleic anhydride; 14.8 parts by weight of phthalic anhydride;6.8 parts by weight of ethylene glycol and 8.7 parts by weight of1,2-propanediol. Of the unsaturated polyester thus obtained 65 parts byweight were mixed with 35 parts by weight of styrene, 2 parts by weightof a 50% by weight solution in water of methyl ethyl ketone peroxide and0.5 parts by weight of a 1% by weight solution in water of cobaltoctoate. Curing was carried out as indicated under Resin 1.

The resin compositions described in the following examples wereinvariably obtained by thoroughly mixing the fire retardant additivesalong with fillers, when utilized, into a mixture of the unsaturatedcompositions. It was then determined that the Fe (salen) and itsoxidation product, [Fe (salen)]₂ O, completely dissolves in the mixture.After the required cross-linking agents had been added, the resincompositions were cured in glass vessels having the dimensionsstandardized for OI (Oxygen Index) bars in accordance with ASTMD2863-70. The results are summarized in the tables. The concentrationsof additives in the form of fire retardant compound and filler areexpressed in grams of additive per 100 grams of resin (thus, thecomponents participating in the curing process, plus additives).

EXAMPLE I

Of the above-mentioned 5 resins the Oxygen Index as a function of the Fe(salen) concentration was determined.

The results are listed in the following Table I.

                  TABLE I                                                         ______________________________________                                        Amount of Fe                                                                  (salen) in g per                                                                              Oxygen Index (OI)                                             Resin No.                                                                             100 g mixture                                                                             Resin   Resin + Fe (salen)                                                                        ΔOI                             ______________________________________                                                0.32        18.7    22.9        4.2                                           1.61        18.7    22.0        3.3                                           3.22        18.7    22.6        3.9                                           6.44        18.7    22.1        3.4                                           9.67        18.7    20.9        2.2                                   2       0.32        19.0    20.1        1.1                                           1.61        19.0    24.2        5.2                                           3.22        19.0    26.8        7.8                                           6.44        19.0    24.1        5.1                                           9.67        19.0    22.7        3.7                                   3       0.32        19.4    21.0        1.6                                           1.61        19.4    23.0        3.6                                           3.22        19.4    22.5        3.1                                           6.44        19.4    22.5        3.1                                           9.67        19.4    22.4        3.0                                   4       0.32        17.7    24.3        6.6                                           1.61        17.7    24.5        6.8                                           3.22        17.7    23.5        5.8                                           6.44        17.7    23.0        5.3                                           9.67        17.7    20.3        2.6                                   5       0.32        18.5    20.0        1.5                                           1.61        18.5    22.0        3.5                                           3.22        18.5    24.9        6.4                                           6.44        18.5    23.9        5.4                                           9.67        18.5    22.7        4.2                                   ______________________________________                                    

EXAMPLE II

The following table gives the results of experiments with 1.61 g Fe(salen) per 100 g resin No. 3 plus Fe (salen), to which also 10 g fillerper 100 g mixture had been added.

                  TABLE II                                                        ______________________________________                                               Oxygen Index                                                                    Resin   Resin + Fe Resin +                                                                              Resin + Fe                                 Filler   No. 3   (salen)    filler (salen) + filler                           ______________________________________                                        Talc     19.4    23.0       19.4   27.3                                       Wollastonite                                                                  (CaSiO.sub.3).sub.3                                                                    19.4    23.0       19.4   27.4                                       CaCO.sub.3                                                                             19.4    23.0       20.3   25.0                                       Mica     19.4    23.0       20.4   25.4                                       TiO.sub.2                                                                              19.4    23.0       20.8   25.3                                       ______________________________________                                    

The above tables clearly demonstrates the considerable synergisticeffect produced on the one hand as a result of the indicated amounts ofFe (salen) and on the other hand as a result of the various fillers.

EXAMPLE III

In this example the results are given of a number of OI-measurements onthe Resins 2 and 3, use having been made of varying amounts of Fe(salen) and filler.

The results are listed in the following table.

                                      TABLE III                                   __________________________________________________________________________    Amount of Fe                                                                  (salen) in g                                                                              Amount of                                                         per 100 g   talc in g                                                                           Oxygen Index                                                    mixture of                                                                            per 100 g           Resin + Fe                                    Resin                                                                             Fe(salen) +                                                                           resin +   Resin +                                                                            Resin +                                                                            (salen) +                                     No. resin   talc  Resin                                                                             Fe(salen)                                                                          talc talc                                          __________________________________________________________________________    2   2.0     10.0  19.0                                                                              25.6 19.0 26.4                                              2.0     40.0  19.0                                                                              25.6 21.0 23.4                                              5.0     10.0  19.0                                                                              24.0 19.0 25.0                                              5.0     40.0  19.0                                                                              24.0 21.0 22.5                                              10.0    10.0  19.0                                                                              22.0 19.0 23.2                                              10.0    40.0  19.0                                                                              22.0 21.0 24.6                                          3   2.0     10.0  19.4                                                                              25.4 19.4 28.3                                              2.0     40.0  19.4                                                                              25.4 20.8 26.5                                              5.0     10.0  19.4                                                                              23.0 19.4 25.0                                              5.0     40.0  19.4                                                                              23.0 20.8 25.8                                              10.0    10.0  19.4                                                                              21.6 19.4 23.6                                              10.0    40.0  19.4                                                                              21.6 20.8 24.0                                          __________________________________________________________________________

EXAMPLE IV (COMPARATIVE EXAMPLE)

In this example the results are given of experiments on the one handwith Fe (salen) and on the other hand with other bis(salicyclidene)ethylene diimino metal compounds. Moreover, the results are includedobtained with other known iron compounds.

The various data are listed in the following table.

The compounds mentioned therein are referred to by their trivial names,and term Co (salen) referring to the cobalt compound, the term Ni(salen) to the nickel compound, and the term Mn (salen) to the manganesecompound.

In all cases the concentration of the fire retardant additive was 2grams per 100 grams of resin plus additive.

The filler was talc. Its concentration was 10 g per 100 g of resin plusfiller.

                                      TABLE IV                                    __________________________________________________________________________                     Oxygen Index                                                                                 Resin + talc                                                           Resin + fire                                                                         + fire re-                                                         Resin                                                                             retardant                                                                            tardant                                       Resin                                                                             Fire retardant compound                                                                    Resin                                                                             + talc                                                                            additive                                                                             additive                                                                             Notes                                  __________________________________________________________________________    2   Fe(salen)    19.0                                                                              19.0                                                                              25.6   26.4   according to                                                                  invention                                  Mn(salen)    19.0                                                                              19.0                                                                              19.2   --                                                Ni(salen)    19.0                                                                              19.0                                                                              19.2   --                                                Co(salen)    19.0                                                                              19.0                                                                              18.9   --                                            3   Fe(salen)    19.4                                                                              19.4                                                                              25.4   28.3   according to                                                                  invention                                  Mn(salen)    19.4                                                                              19.4                                                                              20.0   22.3                                              Ni(salen)    19.4                                                                              19.4                                                                              20.4   20.8                                              Co(salen)    19.4                                                                              19.4                                                                              19.4   21.0                                          2   Fe.sub.2 O.sub.3                                                                           19.0                                                                              19.0                                                                              20.7   --                                                Ferrooxalate 2 H.sub.2 O                                                                   19.0                                                                              19.0                                                                              19.2   --                                                Ferric phosphate                                                                           19.0                                                                              19.0                                                                              18.7   --                                                EDTA-Fe(III) Na                                                                            19.0                                                                              19.0                                                                              19.7   --                                                2,4-pentane dione Fe(III)                                                                  19.0                                                                              19.0                                                                              23.6   --     unsuitable for                             2,4-pentane dione Fe(II)                                                                   19.0                                                                              19.0                                                                              20.0   --     use because of                                                                too rapid curing                           Ferric citrate                                                                             19.0                                                                              19.0                                                                              19.0   --                                                Ferrocene    19.0                                                                              19.0                                                                              --     --     unsuitable be-                                                                cause of inhib-                                                               iting effect on                                                               curing reaction                            Basic ferric acetate                                                                       19.0                                                                              19.0                                                                              21.3   --                                            3   Fe.sub.2 O.sub.3                                                                           19.4                                                                              19.4                                                                              21.0   22.0                                              Ferrooxalate 2H.sub.2 O                                                                    19.4                                                                              19.4                                                                              19.5   20.6                                              Ferric phosphate                                                                           19.4                                                                              19.4                                                                              19.0   20.2                                              EDTA-Fe(III) Na                                                                            19.4                                                                              19.4                                                                              21.2   23.5                                              2,4-pentane-dione-Fe(II)                                                                   19.4                                                                              19.4                                                                              24.0   24.6   Unsuitable be-                                                                cause of too                                                                  rapid curing                           3   2,4-pentane-dione-Fe(III)                                                                  19.4                                                                              19.4                                                                              25.5   26.8   unsuitable be-                                                                cause of too                                                                  rapid curing                               Ferric citrate                                                                             19.4                                                                              19.4                                                                              20.0   20.4                                              Ferrocene    19.4                                                                              19.4                                                                              24.4   25.3   unsuitable be-                                                                cause of inhib-                                                               iting effect on                                                               curing reaction                            Basic ferric acetate                                                                       19.4                                                                              19.4                                                                              20.6   21.9                                          __________________________________________________________________________

The results mentioned in the above table clearly show that the use of Fe(salen) as fire retardant additive in curable ethylenically unsaturatedcompositions based on a compound containing ester groups unexpectedlyleads to far better results than obtained with other known ironcompounds.

What is claimed is:
 1. A composition comprising a curable, ethylenicallyunsaturated compound containing ester linkages and an effective fireretardant amount of an organic iron compound selected from the groupconsisting of N,N'-ethylene bis(salicylidene iminato) Fe II, itsoxidation product, and mixtures thereof.
 2. The composition of claim 1wherein the amount of organic iron compound is from about 0.1 to about10%, by weight, calculated on the mixture of fire retardant additive andcomponents participating in the curing process.
 3. The composition ofclaim 1 or 2 also comprising from about 2 to about 60%, by weight, of afiller, based on the mixture of filler and components participating inthe curing process in the presence of an iron compound which is itselfutilized in an amount from about 0.1 to about 5 percent, by weight,based on the mixture of fire retardant additives and componentsparticipating in the curing process.
 4. The composition of claim 1 alsocomprising from about 5 to about 20 percent, by weight, of filler, basedon the mixture of filler and components participating in the curingprocess, in the presence of an amount of iron compound of 0.1 to 3.5percent, by weight, based on the mixture of iron compound and componentsparticipating in the curing process.
 5. The composition of claim 1, 2,3, or 4, wherein the ethylenically unsaturated compound containing esterlinkages is an unsaturated polyester.
 6. The composition of claim 5 alsocomprising an ethylenically unsaturated monomer which is copolymerizablewith the unsaturated polyester.
 7. The composition of claim 1 alsocomprising an ethylenically unsaturated monomer which is copolymerizablewith the ethylenically unsaturated compound containing ester linkages.8. The composition of claim 1, 2, 3, or 4, wherein the ethylenicallyunsaturated compound containing ester linkages is an unsaturated esterof the following formula: ##STR2## wherein R₁ and R₂ are independentlyselected from the group consisting of hydrogen and methyl, and m and nare integers from about 1.0 to about 3.0.
 9. A process for renderingfire retardant a composition containing a curable, ethylenicallyunsaturated composition containing ester linkages comprising adding tosaid composition an effective fire retardant amount of an organic ironcompound selected from the group consisting of N,N'-ethylenebis(salicylidene iminato) Fe II, its oxidation product, or a mixturethereof.
 10. The process of claim 9 wherein the organic iron compound isutilized in an amount from about 0.1 to about 10%, by weight, calculatedon the mixture of fire retardant additive and components participatingin the curing process.
 11. The process of claim 9 wherein thecomposition also comprises from about 2 to about 60%, by weight, basedon the total weight of the composition, of a filler, based on themixture of filler and components participating in the curing process inthe presence of an iron compound which is itself utilized in an amountfrom about 0.1 to about 5 percent, by weight, based on the mixture offire retardant additives and components participating in the curingprocess.
 12. The process of claim 10 or 11 wherein the compositioncomprises from about 5 to about 20%, by weight, of filler, based on themixture of filler and components participating in the curing process, inthe presence of an amount of iron compound of 0.1 to 3.5 percent, byweight, based on the mixture of iron compound and componentsparticipating in the curing process.
 13. The process of claim 9, 10, or11, wherein the curable, ethylenically unsaturated compound containingester linkages is an ethylenically unsaturated ester of the followingformula: ##STR3## wherein R₁ and R₂ are independently selected from thegroup consisting of hydrogen and methyl, and m and n are integers fromabout 1.0 to about 3.0.
 14. A composition comprising a polymer obtainedby curing a curable, ethylenically unsaturated compound containing esterlinkages and an effective amount of an organic iron compound selectedfrom the group consisting of N,N'-ethylene bis(salicylidene iminato) FeII, its oxidation product, and mixtures thereof.